Red and yellow glaze compositions



Patented June 8, 1937 UNITED STATES aoaaoas nan AND mmowcmzn oomrosrnous Andrew Malinovuky, South Gate, and Albert L. Bennett, Glendale, Calm, aasignora to Malinlte Corporation, of California Los Angeles, (MIL, a corporation No Drawing. Application September I, 1935,

Serial No. 39,622

8 Claims- .(01. ion-3am This invention pertains to compositions which render it possible to obtain brilliant, uniform and stable red glazes on ceramic products. More particularly, the invention relates to the preparation and utilization of selenium or mixtures of selenium and cadmium in glazes and to compositions and methods of operation whereby these stains may be caused to develop brilliant, acidresisting, strong and durable glazes.

Heretofore, selenium or selenium andcadmium mixtures have only been used in glass and in some enamels with indifferent results. In order to develop red tints in ceramic glazes the use of a gold-containing stain or base has been resorted to, the colloidal suspension of gold imparting a ruby tint to the glaze. Pinks and rose-violet shades have been obtained heretofore with chromium and tin but these colors lacked the virility and brilliance of the reds contemplated by this invention. Furthermore, the development of red tints on ceramic bodies has usually necessitated the application of an over-glaze, this procedure adding materially to the costand time spent in the production of the desired ware.

The present invention, on the other hand, utilizes selenium or selenium and cadmium compounds and insures the development of desired shades of red without segregation, the double application of glaze or the exercise of extreme care in temperatures, atmospheric conditions in the muffle or furnace, etc. The colors developed by the glazes of this invention include the yellow, orange and red shown on Plate 3, colors Nos. l7, l5 and 13, on Plate 4, colors Nos. 13, and 17, on Plate 2, colors Nos. '7, 9 and 11 and on Plate I, colors 3, 3i, 5, 5b, 52' and 1, 12, lie of "Color Standards and Color Nomenclature, published by Robert Ridgeway, Washington, D. C. 1912.

It will be seen that these colors distinguish markedly from the pinks, maroons, reds and rose-violet shades previously attainable only by the use of over-glazing or gold suspensions.

The invention also distinguishes from the prior art in that heretofore it was thought essential to have the base or frit substantially free from lead when selenium stains were employed. It has been discovered, however, that the proper manipulation of ingredients in the frit or base not only permits the use of lead but in addition the presence of lead stabilizes the glaze and adds to its brilliance, lack of segregation, and tensile and compressive strength.

It is an object of this invention, therefore, to disclose and provide glaze compositions, frits and stains which are capable of developing brilliant reds upon'maturity upon a ceramic body.

Another object of the invention is to disclose and provide a base or frit capable of being used with selenium stains and of permitting said stains skilled in the art from the following detailed description of preferred compositions, proportions and conditions.

In order to define the terms used herein, it

may be said that in the making of ceramic articles, a base or frit is first prepared by compounding desired ingredients, smelting them or reducing them to vitrified form, and then grinding the fritted or vitrified mass to a state'of fine division. This product is referred to herein as a frit or base. To this base is then added a stain, the stain imparting the color to the otherwise colorless base frit. This invention is particularly directed toward an operation which employs selenium or selenium and cadmium compounds in the stain. Selenium and seleniumcadmium-stains are available on the market at the present time but the present invention also concerns itself with the preparation of a particularly desirable selenium stain which is distinguishable from the stains of the prior art.

The mixture of stain and base frit is then applied to the ceramic bodies which it is desired to provide with a glazed surface. The mixture of frit (this mixture being also referred to as aglaze or glazing mixture) is then applied to the ceramic body either in finely divided dry form or in the form of a suspension or slurry. When the wet method of application is used, various floating mediums may be introduced. The present invention contemplates both dry and wet methods of application.

The glazing mixture is ordinarily applied to bisque bodies, that is, ceramic bodies which have been previously burned to maturity. According to this invention, however, the glazing mixture may be applied either to a high clay bisque which has been burned to a relatively high temperature, or it is applied to either the unburned or burned ceramic body of the character described in a co-pending application filed by Andrew Malinovszky, Serial No. 636,029. p

The body bearing its glazing material is then subjected to the action of heat for the purpose of maturing the glaze, that is, reducing the glazing material to a liquid or semi-liquid, vitrified or glassy condition. when the glazing material has been applied to an unburned body, both the body and the glaze are matured in one operation. The process of this invention contemplates a burning operation which is extremely short or brief, the ceramic body together with its glazing material being subjected to the maximum or maturing temperature for a period of time ranging from 5 minutes to 1 hour only. Furthermore, such maximum'or maturing temperature should be reached very'quickly, that is within a period of time of from 10 minutes to 3 to 4 hours of the time that the body is first exposed to the action of heat. The cooling time may vary considerably but rapid cooling does not deleteriously afiect the preferred glaze, of this invention. The times given are illustrative only and may vary with the type and size of kiln, relation between quantity of ware and the heat supply, concentration of the stain in the glaze, cooling rate, etc. Due to such variables, the time of soaking at the maturing temperatures may be extended to about 2 hours in order to produce the desired result, particularly when the lower maximum temperatures are used. It is to be remembered that the maturity of a body or glaze is a function of temperature and time so that longer times are generally required with lower temperatures and shorter times may be used when higher maximum temperatures are attained.

It has been discovered that whenever selenium or selenium and cadmium compounds are used as stains in a glaze, the glazing material, including the-frit or base, must be carefully compounded certain elements kept out of the frit and other elements introduced into the frit in particular proportions. It has been discovered that alumina, tin and sulphur are injurious to the glazes. Of these three, the most destructive is tin,

the presence of even small quantities, say more than 1.0%-2.0%, of this material making it impossible to obtain a clear red glaze, the color changing into a milky gray, fading out completely or the glaze develops a black, splotchy appearance. Titanium oxide, zirconium oxide, antimony oxide and arsenous oxide, are also deleterious.

Sulphur does not destroy the red .coloration but it is the cause of scumming and imparts to the glaze a dull surface. Alumina has a very destructive efiect on the color, killing the red shade and producing grayish-white to white colors. For this reason it has been definitely demonstrated that the alumina content of the frit or base should be kept below 9% or 10% as these quantities destroy the red coloration. .Preferably, not more than about 5% of alumina should be present and if possible the alumina content is completely eliminated, or at least maintained below about 4%. a

Calcium and magnesium oxides tend to produce segregation of color, dullness,- brownish discoloration, and matted surface and metallic surface effects. When present in small quantities, however, these ingredients are not detrimental. Ordinarily from'2% to 5% 'of the fused frit may consist of calcium .oxide and/or magnesium oxide but the total of these two elements should not exceed 10%.

The silica content of the frit does not appear to influence the color of the selenium glaze.v

Preferably, however, the silica content of the frit lies from. about 46% to 51% as 'frits of this silica content give rise toglazes having good acid resistance. .Somewhat smaller percentages of silica can be used but'not all of the desirable qualities will be simultaneously obtained.

The presence of boron appears essential for the development of true colors with selenium and cadmium. The proportion or boron present in terms of B203 may range from about 7.5% to 30% of the total. Bright red selenium colors will be developed along the entire range but the acid resistance of the resulting glaze is decreased at the higher proportions of boron. Glazes containing more than about 25% of boron have generally been found to have low resistance to acids or even to lemon juice or vinegar. For good acid-resisting glazes, therefore, from about 8% to 14% of boron may be present in the frit. Frits containing from 10% to 14% of boron have the added advantage of minimizing the deleterious effect of relatively high percentages of sodium, zinc, barium, calciumand magnesium. If a sumcient quantity of boron is present, otherwise in- Jurious quantities of these other fluxes may be of sodium needs be present to obtain a sufflcient- 1y low fusingfor maturing temperature for the glaze. The higher amounts of sodium, say from 9% to 12% or more, have been found to cause a certain amount of recrystallization or segregation in certain compositions. The material which crystallizes out of the glaze is a white, water-soluble compound which gives rise to a white discoloration in the glaze. Good results are attained when from 5% to 10% of NaaO and K20 (total) is present.

Although selenium reds of highly desirable brilliance can be obtained by the use of frits high in boron (about 30%), the resulting glazes are not as acid-resisting. It has been discovered, however, that the addition of lead (as lead oxide or carbonate but expressed hereinafter as PbO) not only improves the red colors but also improves the quality of'the glaze itself. The presence of 12% of B203 alone in a frit will not develop the desired selenium red but the addition of lead to the frit causes the development of the desired coloration. A frit containing from 8% to 14% of boron may contain up to about 25% of lead oxide as PbO. Lead in amounts appreciably over 25% exercises a destructive effect on the red color and produces metallic segregations; with certain compositions, the higher contents of lead oxide cause bad boiling of the glaze.

The proportion of lead which-may be added safely to the frit appears to vary directly with the boron content. The higher the boron content. the more lead can be added. The higher. the lead content,,howeve'r, the more yellow the red colors become. It appears that the best glazes as well as the best red colors are obtained when from about 1 to about 2 parts of PhD are presentto each part of B203. When higher proportions of lead to boron are used, there is atendency for aoaaoss Y most satisfactory. Selenium stains may be used asmuch as excellent red glazes have been made without its presence. Titanium and zirconium oxides do not appear to materially influence the color although in any concentration where they become effective as opaciilers they dull the color and texture somewhat. 3% to 5% of either has i been found injurious. Antimony is very destructive to the development of brilliant reds.

The various critical factors mentioned hereinabove may be illustrated in definite frit proportions and analyses. Frits having the-following analysis, for example, will develop a good red color when used with selenium stains:

9 Percent Percent Bio 47 Also- 4. 27 3. 3 CaO. 5. 25} 4 5 0. ll gfio g: 2. 2 (Fr) a NaiO-- 12.12 Bron 21. 32 20. 6 PhD. 0 23.

. red but in addition will be fairly high acid-resisting. Attention is called to the fact that an appreciable quantity of lead has been introduced and the proportion of fluorine present materially reduced.

The following three batches represent highly desirable frits capable of being' used on ceramic bodies for the development of the brilliant selenium colors of this invention. The raw batches may be compounded as follows:

Feldspar l8 l0 Silics 30 23 40 Calcium carbonate. 2 2 0 Magnesium carbonate 4 Borax 19 24 Boric id 6 8 10 Sodium carbonate 5 5 10 Sodium nitrate 3 Calcium fluoride 4 Dsadoxide. i6 24 The above proportions are by weight. The ingredients in each batch are thoroughly mixed and then melted, cooled and ground to give a base having the following analyses:

C D E Attention is called to the fact thatin the preferred frits B, C, D and E, given hereinabove as illustrations, lead and boron are jointly present 5 inthe proportions stated hereinbefore to be in these frits for the development of brilliant and clear red and scarlet colors on ceramic i bodies and furthermore such brilliant reds and scarlets will be developed at maturing temperatures of from about 1650 F. to 1750 F., the time of exposure to these temperatures varyingr only from about 5 to 45 minutes or one hour. In all instances, the maturing temperatures will be below about 2000 F. When the soaking time is extended to say 2 or 3 hours, temperatures as low as 1500 F. are suflioient, the preferred range being from about i550 l". tol800 F. p

, The specific glazes given hereinabove have been used on ceramic bodies of the character described in the co-pending application Serial No.

. 636,029, the glaze being applied to the unburned body and then passed through a tunnel kiln in which the temperature of 1500 F. was reached in 1% hours, a top temperature of 1692 F. reached in,1 hour and 50 minutes, the were leavingthe 1500 F. zone in a little over 2 hours and being cooled down to 400 F. at the expiration of 4 hours from the time the ware entered the kiln. Cone 09 was down in this burning operation. Slightly longer times at lower temperatures are satisfactory.

pheric conditions in the kiln or furnace and for this reason it is not necessary to closely regulate the operation nor insure the presence of either oxidizing or reducing conditions.

It is to be understood that the quantities of the various components may be varied within the limits stated hereinbefore so as to develop a frit having the desired compressive and tensile strength as well as coefliclent of expansion and maturing temperature. It is essential, however, for the successful development of the brilliant colors on ceramic warethat the firing operation be rapid as a long burning operation will turn the above glazes black and finally a milky gray. These selenium glazes, therefore, made in accordance with this invention, can be success fully applied to ceramic bodies not only when the ingredients forming a part of the frit come within the limits defined but also that such frits and glazes be burned under time and temperature conditions which differ widely from those used heretofore.

Whereas days have been heretofore spent in glost burning of ceramic ware, the present operation contemplates the use of hours or minutes only. As a result, not only are unusually brilliant novel colors obtained but furthermore time and cost are decimated and the capacity of a given plant or apparatus enormously increased.

The application of the glazing materials .of this invention on unburned clay bodies is not recommended although they may be applied to well burned clay bisque. Instead of employing a. continuous burning operation as described hereinabove, the ceramic bodies carrying the glazing material may be plunged into a heated zonesuch as a furnace, maintained therein for a. short period of time, say 5 to 30 minutes, and immediately withdrawn into a cooling zone.

When such plunging is used, the heated zone is preferably preheated to a temperature higher than that which would be utilized in maturing the same glaze in a tunnel kiln. For example,

where temperatures of about .l700 F.v are used in a. tunnel kiln, a temperature of about 1850 F.

. should exist in the furnace or'maturing zone before the bodies are plunged thereinto. Obvi- It is to be observed that the glaze is not critically affected by the atmosously, ordinary ceramic bodies will not withstand such rapid temperature changes but the bodies described in'the copending application Serial No. 636,029 are eminently suited for this purpose.

As has been stated hereinbefore, there. are selenium and cadmium stains on the market which may be used with the frits described hereinabove. Better and more uniform results are obtained, however, by preparing the stains in the following manner:

Cadmium, sulfide or carbonate, metallic selenium, zinc oxide or barium carbonate, sulfur and borax (or other .flux such as a small proportion of the frit) are intimately mixed and placed into an air-tight crucible made of dense material such as porcelaim These ingredients in the desired proportions are then calcined in this crucible without access of extraneous air, to a temperature of 900 v('1. to 1000 C., or above the volatilizing temperature of selenium. The calcination is therefore carried out at a superatmospheric pressure and substantially all of the vapors and gases liberated during the operation are retained in the crucible. Excess pressure can. of course, be released during the calcination whenever necessary because of structural characteristics of the apparatus.

During this calcinatlon, the volatilized selenium is thoroughly and intimately absorbed and combined-with the other fluxed ingredients and the calcined stain is retained in the crucible until the temperature thereof has dropped to at least ,600 C. or below the volatilization point of selenium. After finally cooling, the stain is ground and mixed with the base or frit in such proportion that the glazing mixture applied to the ware carries from about /2% to 5% of selenium. The cadmium content may vary from 0% to about 3.5% in terms of cadmium sulfide. In the manufacture of the stain, the following proportions have been found to be particularly suitable:

5 to 35 parts of metallic selenium 25 to 75 parts of cadmium carbonate or cadmium sulfate 10 to 30 parts of sulfur 1 to 4 parts of borax These ingredients are then thoroughly mixed 50 and then compounded with a molecular mixture of silica and boric acid in equal molecular ratios, the mixture of silica and boric acid constituting from about 40% to 60% of the total then added to the calcining crucible.

55 The mixture of cadmium salts, seleniumand borax can also be calcined or frltted with a low fusion alkali boro-zinc-silicate glaze.

Compositions and processes have heretofore been devised for the use of selenium or selenium 60 and cadmium in producing red or orange-colored opaque enamels on metals such as sheet iron,

but this invention relates to .the compositions and processes described above which are capable of producing a transparent brilliant red or orange glaze on a body composed of ceramic materials.

It will be seen by those skilled in the art that a process of producing ceramic bodies provided with brilliant glazes ranging from clear deep 70 reds, through scarlets into the yellow-orange. has been disclosed. This result is attained most successfully as described hereinby preparing selenium stains in the manner stated, compounding the frit with boron and lead and in 7 the substantial absence of alumina and tin and then burning ceramic bodies containing silica and alkaline earths in major proportions (of the character described in the co-pending application Serial No. 636,029) to a maturing temperature quickly, that is, so as to cause the glazing material to reach the maturing temperature in from 10 minutes to not more than about 4 hours.

This application is a division of aco-pendingapplication Serial No. 665,442 relating to the process of utilizing the frits and stains herein described. Those skilled in the art will appreciate that numerous changes, modifications and adaptations of this invention may be made without departing from the novel teachings of this invention. All such changes and modifications as come within the scope of the appended claims are embraced thereby.

We claim:

l. A ceramic frit for use with selenium and cadmium stains on ceramic bodies, capable .of developing brilliant red, scarlet and orange colors at maturing temperatures below about 2000 F., said frit containing from about 7.5% to 30% of B203, about 7.5% to 25% of PbO, about 5% to 12% of Na20, not more than about 10% of A1203, not more than about 3% of F2, the balance being composed principally of silica and the frit being practically free from tin.

2. A glazing composition capable of developing clear and substantially transparent colors at maturing temperatures below about 2000 F., said glazing composition comprising a frit intermixed with a stain, said frit containing from about 7.5% to 30% of B203, about 7.5% to 25% of PhD, about 5% to 12% of No. 0, not more than about 10% of A1203, not more than about 3% of F2, and practically free from tin, the balance being composed principally of silica, said stain beingcomposed principally of selenium,'cadmium and flux and resulting from the calcination of cadmium,selenium and flux without access to air at a temperature above the volatilizing temperature of selenium.

3. A glazing composition capable of developing clear and substantially transparent colors at maturing temperatures below about 2000 F.,

I said glazing composition comprising a frit intermixed with a stain, said frit containing from about 7.5% to 30% of B203, about 7.5% to 25% of vPbO, about 5% to 12% of Na20, not more than about 10% of A1202, not more than about 3% of F2, and practically free from tin, the balance being composed principally of silica, said stain being present in quantities suilicient to introduce from about 0.5% to-5% of selenium by weight.

4. A glazing composition capable of developing clear and substantially transparent colors at maturing temperatures below about 2000 F., said glazing composition comprising a frit intermixed with a stain, said frit containing from about 7.5% to 30% of B203, about 7.5% to 25% of PbO, about 5% to 12% of Na2O, not more than about 10% of A1202, notmore than about 3% of F2, and practically free from tin, the balance helm composed principally of silica, said stain being present in quantities suflicient to introduce from about 0.5% to 5% of selenium and up to about 3.5% of cadmium by weight.

5. 'A ceramic frit adapted for use with selenium stains on ceramic bodies to develop substantially transparent colorsat maturing temperatures below about 2000 F., said frit containing from about 7.5% to 25% of B203, about 10% to 22% of PbO, not more than about 5% of A1203, and'being practically free from tin, the balance being composed principally of silica.

6. A ceramic frit adapted for'use with selenium stains on ceramic bodies and capable of developing substantially transparent colors at maturing temperatures below about 2000 F., said frit containing from about 7.5% .to 30% of B203, about 7.5% to 25% of PhD, not more than about 5% of A1203, not more than about 3% of F2, and being practically free'from tin, the balance being composed principally of silica.-

7. A glazing composition capable of developing brilliant red, scarlet and orange'colors on ceramic bodies at maturing temperatures below about 2000 F., said glazing composition comprising a frit containing from about 7.5% to 30%' oil B203, about 7.5% to 25% of PbO, not more than about 5% of A1203, not more than about 3% of F2, and being practically free from tin, the

balance being composed principally of silica, and a selenium stain intermixed with said frit in quantities suflicient to introduce from about 0.5% to 5% of selenium by weight.

8. A glazing composition capable of developing brilliant red, scarlet and orange colors on ceramic bodies at maturing temperatures below about 2000 F., said glazing composition comprising a frit containing from about 7.5% to 30% of B203, about 7.5% to 25% of PbO, not more than about 5% of A1203, not more than about 3% of F2, and being practically free from tin, the balance being composed principally. of silica, and a stain intermixed with said frit, said stain being present in quantities sufiicient to introduce from about 0.5% to 5% of selenium and up to about 3.5% of cadmium by weight.

ANDREW MALINOVSZKY.

ALBERT L. BENNE'I'I. 

